The long term objective of the proposed study is to develop a miniaturized electrochemical detector, based on the hydrated solid polymer electrolyte for transdermal alcohol measurements to monitor treatment compliance. The specific aims of this Phase II proposal are to 1) optimize the sensor cell diffusion control and electronic control/recorder functions, 2) develop wearable, passive prototype sensor/recorder devices, and 3) implement a protocol to evaluate the advanced prototype devices for transdermal monitoring of a significant number of subjects in clinical testing. The methodology is to 10 identify a rate limiting membrane for the sensor cell, 20 develop an efficient low current and sensitive electronic circuit, 3) develop a miniaturized solid state recorder, and 40 package the components into a unitized prototype device to be worn by human subjects in transdermal alcohol studies, conducted in collaboration with Roger Williams Hospital. The proposed solid polymer electrolyte electrochemical sensor and diffusion control system are a novel concept, specifically designed for long term transdermal alcohol measurements. Also, the proposed miniaturized microcontroller/recorder system, which stores data and gives an historical of alcohol consumption, has potential for technical innovation.